How to make two alembic Mesh Sequence Caches working together
Blender Sushi Guy here, I encountered the exact same situation today. And I think I have a solution that is using Sverchok nodes, but easily translateable into Drivers or Python code solution. I think Dr. Sybren can help :)



So, I have multiple alembic cace file, each for 1000 frames. I broken down the Alembic sequence into multiple caches because 10000 frames == keeps crashing Blender.

Anyhow, just like what you are trying to do, you want to "mix" the Alembic cache together, using Modifier stacks.

Ideally, there should be a mechanism in Blender allowing to do this. Maybe Blender devs are still working on it(?).

For now, I am using this "simple trick" that is basically triggering the "show_viewport" ON and OFF as needed.

I have 2 caches here, cache A (frame 1-1000) and cache B (frame 1001-2000). You can have more.

Both has "Override Frame" turned on. So we will be controlling the frame using "Time Frame". That part is taken care of.

But as you mentioned, once you stack multiple cache, the second will completely override the previous. 

However if you control the "show_viewport" and trigger ON and OFF at the right time (in this case I am using nodes logic to check frame number, if frame number is bigger than > 1000, then 2nd cache SHOULD take over and continue the cache. Otherwise, it should run the 1st cache first.

Let say we have 3,4,5 cache, we can use similar logic. 

I test a quick OpenGL render and seems like my cache A and B mixed together into the same mesh.

I wonder what Blender Devs working on Alembic can say about this.

But that is one solution.

Perhaps "Use Modifier During Render" (the camera icon) also needs to be triggered.



The easiest is to use Drivers, for this. In my case, I am relying on nodes.